Airline passengers have recently been given the opportunity of making telephone calls from airplanes. Presently the cost for making such calls is relatively high. However, as in most applications of communication systems, the cost for making the calls will decrease, and more people will use the system. However, the frequency allocated for air to ground communications is a relatively limited (narrow) spectrum, hence the spectrum will soon become overcrowded thereby resulting in substantial delays for establishing telephone communications.
There are various techniques and methods for more efficiently utilizing the available spectrum assigned to each communications medium. A recent improvement in cellular technology generally has been the provision of digital modulation schemes which effect a significant increase in spectral capcity. Another recent improvement in cellular technology to date has been the provision of patterns of directional antennas that permit tight reuse patterns. The extra dB of interference protection offered by such antennas permits some ingenius patterns that are very efficient with respect to frequency reuse.
Still another innovation of importance in cellular technology is the method of "cell splitting". Basically, users very near their base sites do not need as much signal to noise protection so that these users can be combined into sets with different safety factors and cell patterns, as compared to users who are far away from their base sites.
One of the most important improvements in cellular communication is the recently developed system that provides frequency assignment independently of pre-set geographical cell patterns. The system performs calculations in real time to optimally allocate the channels to achieve the greatest of all frequency spectrum utilization. This system operates with actual signal strengths received, as opposed to a preplanned cellular pattern, and thus permits a totally freeform assignment that fully utilizes the allocated spectrum. The digital modulation schemes mentioned above can be utilized with this latter system to achieve spectrum utilization factors of eight or more to one compared to the prior art systems.